Commit message: openvswitch: fix OOB access in reserve_sfa_size()

Given a sufficiently large number of actions, while copying and
reserving memory for a new action of a new flow, if next_offset is
greater than MAX_ACTIONS_BUFSIZE, the function reserve_sfa_size() does
not return -EMSGSIZE as expected, but it allocates MAX_ACTIONS_BUFSIZE
bytes increasing actions_len by req_size. This can then lead to an OOB
write access, especially when further actions need to be copied.

Fix it by rearranging the flow action size check.

KASAN splat below:

==================================================================
BUG: KASAN: slab-out-of-bounds in reserve_sfa_size+0x1ba/0x380 [openvswitch]
Write of size 65360 at addr ffff888147e4001c by task handler15/836

CPU: 1 PID: 836 Comm: handler15 Not tainted 5.18.0-rc1+ #27
...
Call Trace:
 <TASK>
 dump_stack_lvl+0x45/0x5a
 print_report.cold+0x5e/0x5db
 ? __lock_text_start+0x8/0x8
 ? reserve_sfa_size+0x1ba/0x380 [openvswitch]
 kasan_report+0xb5/0x130
 ? reserve_sfa_size+0x1ba/0x380 [openvswitch]
 kasan_check_range+0xf5/0x1d0
 memcpy+0x39/0x60
 reserve_sfa_size+0x1ba/0x380 [openvswitch]
 __add_action+0x24/0x120 [openvswitch]
 ovs_nla_add_action+0xe/0x20 [openvswitch]
 ovs_ct_copy_action+0x29d/0x1130 [openvswitch]
 ? __kernel_text_address+0xe/0x30
 ? unwind_get_return_address+0x56/0xa0
 ? create_prof_cpu_mask+0x20/0x20
 ? ovs_ct_verify+0xf0/0xf0 [openvswitch]
 ? prep_compound_page+0x198/0x2a0
 ? __kasan_check_byte+0x10/0x40
 ? kasan_unpoison+0x40/0x70
 ? ksize+0x44/0x60
 ? reserve_sfa_size+0x75/0x380 [openvswitch]
 __ovs_nla_copy_actions+0xc26/0x2070 [openvswitch]
 ? __zone_watermark_ok+0x420/0x420
 ? validate_set.constprop.0+0xc90/0xc90 [openvswitch]
 ? __alloc_pages+0x1a9/0x3e0
 ? __alloc_pages_slowpath.constprop.0+0x1da0/0x1da0
 ? unwind_next_frame+0x991/0x1e40
 ? __mod_node_page_state+0x99/0x120
 ? __mod_lruvec_page_state+0x2e3/0x470
 ? __kasan_kmalloc_large+0x90/0xe0
 ovs_nla_copy_actions+0x1b4/0x2c0 [openvswitch]
 ovs_flow_cmd_new+0x3cd/0xb10 [openvswitch]
 ...

Cc: stable@vger.kernel.org
Fixes: f28cd2af22a0 ("openvswitch: fix flow actions reallocation")
Signed-off-by: Paolo Valerio <pvalerio@redhat.com>
Acked-by: Eelco Chaudron <echaudro@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
CVE: CVE-2022-2639
CWE: CWE-362
Vulnerability description: An integer coercion error was found in the openvswitch kernel module. Given a sufficiently large number of actions, while copying and reserving memory for a new action of a new flow, the reserve_sfa_size() function does not return -EMSGSIZE as expected, potentially leading to an out-of-bounds write access. This flaw allows a local user to crash or potentially escalate their privileges on the system.

Project: linux
File: flow_netlink.c

static struct nlattr *reserve_sfa_size(struct sw_flow_actions **sfa,
				       int attr_len, bool log)
{

	struct sw_flow_actions *acts;
	int new_acts_size;
	size_t req_size = NLA_ALIGN(attr_len);
	int next_offset = offsetof(struct sw_flow_actions, actions) +
					(*sfa)->actions_len;

	if (req_size <= (ksize(*sfa) - next_offset))
		goto out;

	new_acts_size = max(next_offset + req_size, ksize(*sfa) * 2);

	if (new_acts_size > MAX_ACTIONS_BUFSIZE) {
		if ((MAX_ACTIONS_BUFSIZE - next_offset) < req_size) {
			OVS_NLERR(log, "Flow action size exceeds max %u",
				  MAX_ACTIONS_BUFSIZE);
			return ERR_PTR(-EMSGSIZE);
		}
		new_acts_size = MAX_ACTIONS_BUFSIZE;
	}

	acts = nla_alloc_flow_actions(new_acts_size);
	if (IS_ERR(acts))
		return (void *)acts;

	memcpy(acts->actions, (*sfa)->actions, (*sfa)->actions_len);
	acts->actions_len = (*sfa)->actions_len;
	acts->orig_len = (*sfa)->orig_len;
	kfree(*sfa);
	*sfa = acts;

out:
	(*sfa)->actions_len += req_size;
	return  (struct nlattr *) ((unsigned char *)(*sfa) + next_offset);
}